<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    li{
      height: 40px;
      width: 400px;
      background-color: #e7c3c3;
      margin-top: 10px;
    }
  </style>
</head>
<body>
  <div id="app">
      <button @click="addLi">新增li</button>
      <ul>
        <li v-for="item in arr" :key="item">
          {{item}}
        </li>
      </ul>
  </div>
  
  <script src="./vue.global.js"></script>
  <script>
    const { createApp } = Vue;
    const app = createApp({
      data(){
        return {
          arr: [1,2,3,4]
        }
      },
      methods: {
        addLi() {
          this.arr.push(this.arr.length+1);
          const oul = document.querySelector('ul');
          // oul.lastElementChild.style.background = 'red';
          this.$nextTick(() => {
            // 在每一次 视图更新完成后触发
            console.log(oul.children);
            oul.lastElementChild.style.background = 'red';
          })
          console.log(2);
        }
      },
    })
    app.mount('#app')
  </script>
</body>
</html>